A display device uses a plurality of pixel units for displaying, and each pixel unit comprises a pixel circuit.
FIG. 1 illustrates a schematic circuit diagram of a conventional pixel circuit. A plurality of pixel circuits, P11, P12, P21, P22, having a same structure are shown in FIG. 1. Take the pixel circuit P11 as an example. The pixel circuit P11 comprises a transistor T11, which connects or disconnects the data line D1 with/from the storage cell C11 under the control of a signal from the gate line G1.
FIG. 2 illustrates a schematic diagram of a signal waveform of a conventional pixel circuit. As shown in FIG. 2, the vertical axis V represents the voltage amplitude of the signal applied to the gate of the transistor T11, and the horizontal axis T represents the time, where VGH represents the high level at which the transistor T11 is turned on, and VGL represents the low level at which the transistor T11 is turned off. During the display of an image by a display device, the transistor T11 is switched between ON and OFF states, and the transistor T11 maintains in an OFF state for a long the time (about 99% of the time). Being in an OFF state for a long time will cause the threshold voltage of the transistor T11 to shifted negatively, which, if severe, would damage the transistor T11, causing the pixel circuit P11 operate abnormally.
It is desired to improve the pixel circuit and the shift register unit for driving the pixel circuit.